Such raw-material mixtures for instance contain oil sands and oil shale.
Oil sands and oil shale are sedimentary rocks that occur worldwide and depending on where they are located contain from 5 mol-% to 65 mol-% organic substance, known as kerogen.
A mixture of clay, silicates, water and hydrocarbons is called oil sand. Because of this mineralogical composition, oil sands have high proportions of SiO2, CaCO3, Al2O3, and Fe2O3.
The inorganic ingredients of oil shale are essentially clay materials, quartz and feldspar, as well as various proportions of CaO-containing compounds, in particular calcite containing lesser amounts of dolomite and/or gypsum. The result is an oxidic composition similar to oil sands. Because of its chemical-mineralogical composition, burned oil shale has long been known in the cement industry as a hydraulic binder or at least as a hydraulic additive.
Oil shale ash exhibits a wide fluctuation in its chemical composition, depending on where it is found:
IngredientConcentration range in %SiO212 . . . 51Al2O3 5 . . . 16Fe2O36 . . . 7CaO18 . . . 60MgO1 . . . 4Na2O + K2O1 . . . 2SO3 5 . . . 10
Thus burned oil shale, at low Ca contents, comprises calcined clay with pozzolanic properties, with sufficiently high CaO contents, particularly from dicalcium silicate and calcium aluminates. In the cement industry, these phases are known as carriers of the hydraulic qualities and are produced intentionally.
Among other things, burned oil shale is included in the European and German cement standards under the designation CEM II-T, according to DIN [German Industrial Standard] EN 196. With a compressive strength of at least 25 N/mm2 when stored in humid air after 28 days, the burned oil shale is a primary ingredient in Portland shale cement.
In burning oil shale/sands, its high proportion of sulfur is problematic, as is the fact that because of the heterogeneous composition of the starting material, the burning methods used until now were not suitable for producing high-value binders of varying types.